DesignSpark have published some good-looking resources for teachers to use in the classroom to help students learn about the GPIO. They are as follows:

• Program a seven-segment display.
• Read digital signals and analogue signals (via an A2D chip) and how to generate an analogue output.
• Read a one-wire temperature sensor and then output the reading to a multiple-digit LED display.
• Controlling a motor using a L293D driver chip.

They look good-quality documents with plenty of Fritzing circuit diagrams to help you. Each resource comes with worksheets for students and classroom notes for teachers.

Take a look at the resources here (the site is a little slow, so bear with it).